CommunicatingwithaServer

TheCloud

ClientandServer• Mostmobileapplicationsarenolongerstand-alone• Manyofthemnowhavea“Cloud”backend

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DatabaseServerBackendClient-servercommunication

HTTPwithRESTAPI

TheNetworkingAlphabetSoup

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HTTPURL JSONXMLSOAP RESTGETPOST PUT

AndroidNetworking• Networkoperationscauseunexpecteddelays• Alwaysdonetworkoperationsinthebackground– UseAsyncTask()orbackgroundthread– AndroidwillcauseexceptionifyoudonetworkingoperationsonthemainUIthread

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Offtothenextexercise• ProcessingaJSONstring• MappingJSONstringtoJavaObjects• UsingGson library

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Javascript ObjectNotation(JSON)

HTTPResponse• Servermaysendbackinformation inaspecificformat:

– eXtensible MarkupLanguage(XML)– Javascript ObjectNotation(JSON)

• Android alsoincludesthreeparsersforXMLandaparserforJSON– thetraditionalW3CDOMparser(org.w3c.dom)– convertsdocumenttoatreeofnodes– aSAXparser(org.xml.sax)– streamingwithapplicationcallbacks– theXMLpullparser– iteratesoverXMLentries– JSONparser(org.json)

• Alsoconsider theuseofthird-partylibrariestodealwithspecificformatslikeRSS/Atomparser

• Gson librariestoconvertfromJavaobjectstoJSONandback

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Javascript ObjectNotation(JSON)• http://www.json.org• Lightweightdatainterchange format• Languageindependent*• Self-describingandeasytounderstand• Datastructuredas:

– Acollectionofname/valuepairs– Orderedlistofvalues– Example

{"people":[{"id":1,"name":"John”,"statusMsg": "Imagineallthepeople...”,"imageURL":"John.png”},{"id":2,"name":"Paul”,"statusMsg": "Letitbe...”,"imageURL":"Paul.png”},{"id":3,"name":"George”,"statusMsg": "Waitmisterpostman...”,"imageURL":"George.png" },{"id":4,"name":"Ringo”,"statusMsg": "Yellowsubmarine...”,"imageURL":"Ringo.png”}

]}

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Offtothenextexercise• UsinganAsyncTask tooffloadworkfromthemainUIthread

• UsingPicassoimagedownloadinglibrary

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AsyncTask:DoingWorkintheBackground

Threads/AsyncTask

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UIThread BackgroundThread

Spawnbackground threadorUseAsyncTask

ReturnresultToupdateUICodeto

RunonUIthread

AsyncTask• Threadsprovidesapowerfulframework– Codegetscomplicatedanddifficulttoread

• AsyncTask:simplifiesthecreationoflong-runningtasksthatneedtocommunicatewiththeUI– Takescareofthreadmanagement– HastobecreatedontheUIthread

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AsyncTask• AsyncTask hasthefollowingexcellentfeatures:– Abilitytoreturnvalues ofcustomtypetotheUIthreadwhenthetaskisfinished

– AbilitytoexecutesomecodeintheUIthread beforethebackgroundtaskbeginsexecutionandafteritisfinished

– Abilitytopushupdates totheUIthreadduringtheexecutionofthebackgroundtask

– Automatic under-the-hoodthreadmanagement

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AsyncTask Exampleprivate class WorkerTask extends AsyncTask {

//InitializetheprogressbarandthestatusTextView@Overrideprotected void onPreExecute() {

completed =0;//ThiswillresultinacalltoonProgressUpdate()publishProgress();

}

@Override//ThismethodupdatesthemainUI,refreshing theprogress barandTextView.protected void onProgressUpdate(String... values){

}

//Dothemaincomputation inthebackgroundandupdatetheUIusingpublishProgress()@Overrideprotected Boolean doInBackground(Object...params){

return null;}

}COMP107x(Muppala) AndroidNetworking 14

AsyncTask• SeveralmethodsarepartofAsyncTask:

– doInBackground()executesautomaticallyonaworkerthread– onPreExecute(),onPostExecute(),andonProgressUpdate()areall

invokedontheUIthread– CallpublishProgress()atanytimeindoInBackground()toexecute

onProgressUpdate()ontheUIthread– ThevaluereturnedbydoInBackground()issenttoonPostExecute()– Youcancancelthetaskatanytime,fromanythread

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Offtothenextexercise• ConnectingtoaserverusingHTTPURLconnection

• GettingJSONstringfromtheserver

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AndroidNetworking

AndroidPermissions• SetpermissionintheManifestfile:

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AndroidConnectivityManager• AndroidprovidestheConnectivityManagerclasstomonitornetworkconnectivitystate,settingpreferrednetworkconnectionsandmanagingconnectivityfailover

• GetaccesstotheConnectivityManager by:ConnectivityManagermyNetMan =(ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);

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AndroidConnectivityManager• ConnectivityManagerprovidesmethodslikegetNetworkInfo(),getActiveNetworkInfo(),andgetAllNetworkInfo()etc.– ThesemethodsreturntheNetworkInfo object– CanusemethodswithinthisobjectlikeisAvailable(),isConnected,isConnectedorConnecting(),getState(),etc.

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AndroidConnectivityManager• Ifyouareusingthenetworkaccessinyourapplication,itisalwaysagoodideatocheckifthe

networkconnectivityexists,andtakeactionaccordingly• Example

public boolean isOnline() {ConnectivityManager connMgr =(ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkInfo networkInfo =connMgr.getActiveNetworkInfo();

if(networkInfo !=null&&networkInfo.isConnected()) {returntrue;

}else{returnfalse;

}}

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AndroidHTTPSupport

AndroidandHTTP• AndroidprovidesHTTPURLConnection clienttosendandreceive

dataovertheweb• AndroidalsohasApacheHTTPcomponentslibrarybuiltintothe

framework– HttpClient componentenableshandlingofHTTPrequestsonyour

behalf,issuingHTTPrequestsanddealingwiththeresponse– Notthepreferredchoiceanymore

• YoucanlayeraSOAP/XML-RPClayeratopthislibraryoruseit"straight"foraccessingREST-stylewebservices

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AndroidHTTPURLConnection ExamplefinalStringsite="http://:3000/people";

//gettheURLconnectionURLurl =newURL(site);HttpURLConnection urlConnection =(HttpURLConnection)url.openConnection();

//setup theURLrequestparametersurlConnection.setReadTimeout(10000/*milliseconds*/);urlConnection.setConnectTimeout(15000 /*milliseconds*/);urlConnection.setDoInput(true);

/*optionalrequestheader*/urlConnection.setRequestProperty("Content-Type", "application/json");urlConnection.setRequestProperty("Accept", "application/json");

/*forGetrequest*/urlConnection.setRequestMethod("GET");

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AndroidHTTPURLConnection Example//Startsthequeryint statusCode =urlConnection.getResponseCode();Log.d(DEBUG_TAG,"Theresponseis:"+statusCode);

//getthe inputstreamfortheresponsebodyoftheURLresponseInputStream inputStream =new

BufferedInputStream(urlConnection.getInputStream());

//parsetheresponseStringresponse=convertInputStreamToString(inputStream);parseResult(response);

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Assignment5:AsynchronousDownloadofImages

• UsePicassolibrarytodownloadtheimagesasynchronouslyandupdatetheListViewavatarsoftheusers

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